Optical information recording medium offset pre-pit array indicating identification information

ABSTRACT

An optical information recording medium according to the present invention includes at least one groove track and at least one land track allowing information to be recorded on or reproduced from the groove track and the land track, the groove track and the land track adjoining each other. The optical information recording medium further includes: an identification signal region including a pre-pit array, the pre-pit array indicating identification information concerning the groove track and the land track; and a servo control region disposed ahead of the identification signal region along the groove track and the land track, the servo control region including wobble pits positioned so as to shift to opposite sides of a center line of either the groove track or the land track.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to: an optical information recordingmedium which utilizes both groove regions (i.e., guide grooves) and landregions (i.e., regions between grooves) as information tracks, thegrooves and lands having been previously formed on the opticalinformation recording medium; and an optical informationrecording/reproduction device for recording an information signal on theoptical information recording medium.

2. Description of the Related Art

In recent years, there have been vigorous research and developmentactivities for realizing optical information recording media forrecording and reproducing information signals (e.g., video signals andaudio signals) thereon. One example of such an optical informationrecording medium is an optical disk. A recordable optical disk includesguide grooves (hereinafter referred to as "grooves") previously engravedon a substrate, the grooves constituting information tracks. Any regionbetween adjoining grooves is referred to as a "land". Informationsignals can be recorded or reproduced on the optical disk by converginga laser light beam on the flat portions of grooves or lands.

In the case of common commercially-available optical disks, informationsignals are typically recorded on either grooves or lands. Wheninformation signals are recorded on the grooves, for example, the landsserve as guard bands for separating adjoining tracks defined by thegrooves. In the case where information signals are recorded on thelands, the grooves serve as guard bands.

FIG. 9 is a magnified perspective view of a conventional optical diskhaving the above-mentioned structure. In FIG. 9, reference numeral 85denotes a recording layer (which may be composed of a phase-changematerial, for example); 86 denotes a recording pit; 87 denotes a laserbeam spot; 88, 90, and 92 denote guide grooves defining "grooves"; 89and 91 denote "lands"; 93 denotes a transparent substrate through whichlight enters. As seen from FIG. 9, grooves are made wider than lands inthis exemplary conventional optical disk.

In an attempt to increase the recording capacity of the aboveconventional optical disk, the interspaces between tracks are shortenedby narrowing the widths of the lands 89. However, a smaller interspacebetween tracks results in a larger diffraction angle of light reflectedfrom the grooves. This results in a lower level of tracking errorsignal, which is employed to ensure accurate tracing of the beam spot 87on the tracks.

Moreover, there is a limit to the increase in track density achieved bymerely reducing land widths. However, reducing the groove widths mightlower the amplitude of the reproduced signal due to thinner recordingpits 86.

On the other hand, there are techniques for increasing the trackdensity, such as that disclosed in Japanese Patent Publication No.63-57859, according to which information signals are recorded on bothgrooves and lands.

FIG. 10 is a magnified perspective view of such an optical disk. In FIG.10, reference numeral 85 denotes a recording layer; 86 denotes arecording pit; 87 denotes a laser beam spot; 93 denotes a transparentsubstrate; 94, 96, and 98 denote grooves; 95 and 97 denote lands.

As shown in FIG. 10, the grooves and the lands have substantially thesame width. Pre-pits 99, which are formed for both grooves and lands,are engraved at the beginnings of sectors of both information tracks(i.e., groove and lands) as identification signals representinglocational information on the optical disk.

In the above optical disk, the recording pits 86 are formed for bothgroves and lands as shown in FIG. 10. Although the grooves have a periodequal to the period of grooves in the optical disk shown in FIG. 9, eachinterspace between adjoining recording pit rows in FIG. 10 is half ofthat of the optical disk shown in FIG. 9. As a result, the optical diskin FIG. 10 has twice as large a recording capacity as that of theoptical disk in FIG. 9.

Rewritable optical disks require identification signals (indicatinglocation information on the disk), etc., to be previously recorded onthe disk. The inventors of the present invention have proposed inJapanese Laid-Open Patent Publication No. 6-176404 a technique ofrecording one identification signal for an adjoining pair consisting ofa groove and a land so as to be located between the groove and the land.

However, in the above-mentioned optical information recording media, thetrack pitch is reduced to half of that of conventional opticalinformation recording media, thereby requiring an even more accuratetrack servo control. Particularly when an identification signal isrecorded between a land and its corresponding groove, only one half ofthe beam spot will be incident on the pre-pits. Therefore, when the beamspot shifts away from the track center, toward regions where theidentification signal is not present, it may be impossible to detect theidentification signal.

SUMMARY OF THE INVENTION

An optical information recording medium according to the presentinvention includes at least one groove track and at least one land trackallowing information to be recorded on or reproduced from the groovetrack and the land track, the groove track and the land track adjoiningeach other, wherein the optical information recording medium furtherincludes: an identification signal region including a pre-pit array, thepre-pit array indicating identification information concerning thegroove track and the land track; and a servo control region disposedahead of the identification signal region along the groove track and theland track, the servo control region including wobble pits positioned soas to shift to opposite sides of a center line of either the groovetrack or the land track.

In one embodiment of the invention, the wobble pits include a pluralityof pairs of pre-pits positioned so as to shift to opposite sides of thecenter line.

In another embodiment of the invention, the plurality of pairs ofpre-pits indicate a reproduction synchronization signal.

In still another embodiment of the invention, a synchronization signalsection indicating the beginning of the wobble pits is providedimmediately before the wobble pits, and the synchronization signalsection includes a pit array positioned on the center line of either thegroove track or the land track.

In still another embodiment of the invention, at least a portion of thepre-pit array in the identification signal region is formed so as to beshifted away from the center line of either the groove track or the landtrack.

In still another embodiment of the invention, the identification signalregion includes a pit indicating a track identification signal.

In still another embodiment of the invention, the pit indicating thetrack identification signal is shifted away from the center line ofeither the groove track or the land track.

In still another embodiment of the invention, the groove track and theland track are divided into a plurality of sectors, the pre-pit array inthe identification signal region includes an address pit arrayindicating address information of a corresponding sector.

In still another embodiment of the invention, the groove track and theland track are formed in a spiral or concentric shape on a disksubstrate.

In still another embodiment of the invention, the identificationinformation includes a track number.

In still another embodiment of the invention, a portion of the pre-pitarray indicating the identification signal that indicates the tracknumber is shifted away from the center line of either the groove trackor the land track along a direction across the groove track and the landtrack.

In still another embodiment of the invention, pre-pits in the pre-pitarray indicating the identification signal which are formed so as to beshifted away from the center line of either the groove track or the landtrack are shifted away from the center line of either the groove trackor the land track by about 1/4 of a track pitch.

In still another embodiment of the invention, an optical depth or heightof the pre-pit array indicating the identification signal issubstantially equal to the depth of the groove track.

In still another embodiment of the invention, an optical depth or heightof the pre-pit array indicating the identification signal issubstantially equal to λ/4 (where λ represents the wavelength of a lightbeam)

In still another embodiment of the invention, the width of the pre-pitarray indicating the identification signal is substantially equal to thewidth of the groove track.

In still another embodiment of the invention, the width of the pre-pitarray in the synchronization signal or the pre-pit array indicating theidentification signal is larger than the width of the groove track.

In still another embodiment of the invention, a gap section is providedbetween the servo control region and the identification signal region.

In still another embodiment of the invention, the optical informationrecording medium further includes a rewritable recording layer, whereinthe recording layer is formed of a phase-change type material capable oftaking an amorphous state or a crystal state.

In another aspect, the present invention provides an optical informationrecording/reproduction device for recording/reproducing information witha light beam on an optical information recording medium including atleast one groove track and at least one land track allowing informationto be recorded on or reproduced from the groove track and the landtrack, the groove track and the land track adjoining each other, and theoptical information recording medium further including: anidentification signal region including a pre-pit array, the pre-pitarray indicating identification information concerning the groove trackand the land track; and a servo control region disposed ahead of theidentification signal region along the groove track and the land track,the servo control region including wobble pits positioned so as to shiftto opposite sides of a center line of either the groove track or theland track, and the optical information recording/reproduction deviceincluding: an optical system for allowing the light beam emitted from alight source to be incident on the optical information recording medium;transportation means for moving the relative position of a light spot onthe optical information recording medium created by the light beam alonga direction in which the groove track and the land track extend; lightdetection means for receiving reflected light of the beam spot from theoptical information recording medium in a plurality of light receivingportions and for converting the reflected light into an electric signalwhich is output as a light detection signal; identification signalreading means for reproducing the identification signal from the lightdetection signal; a first tracking error detection circuit fordetecting, while the optical spot travels on the groove track or theland track, a shift amount of the optical spot with respect to thecenter line and for outputting a first error signal indicating the shiftamount; a second tracking error detection circuit for detecting, whilethe optical spot is travelling over the servo control region, a shiftamount of the optical spot with respect to the center line by detectingthe intensity of returned light from the wobble pits and for outputtinga second error signal indicating the shift amount; a correction circuitfor outputting a tracking signal obtained by correcting the first errorsignal based on the second error signal; and a tracking controller forcontrolling the transportation means to cause the beam spot to travelover the groove track or the land track based on the tracking signal.

Alternatively, the present invention provides an optical informationrecording/reproduction device for recording/reproducing information witha light beam on an optical information recording medium including atleast one groove track and at least one land track allowing informationto be recorded on or reproduced from the groove track and the landtrack, the groove track and the land track adjoining each other, and theoptical information recording medium further including: anidentification signal region including a pre-pit array, the pre-pitarray indicating identification information concerning the groove trackand the land track; and a servo control region disposed ahead of theidentification signal region along the groove track and the land track,the servo control region including wobble pits positioned so as to shiftto opposite sides of a center line of either the groove track or theland track; and a synchronization signal section indicating thebeginning of the wobble pits, the synchronization signal section beingprovided immediately before the wobble pits and including a pit arraypositioned on the center line of either the groove track or the landtrack, and the optical information recording/reproduction deviceincluding: an optical system for allowing the light beam emitted from alight source to be incident on the optical information recording medium;transportation means for moving the relative position of a light spot onthe optical information recording medium created by the light beam alonga direction in which the groove track and the land track extend; lightdetection means for receiving reflected light of the beam spot from theoptical information recording medium in a plurality of light receivingportions and for converting the reflected light into an electric signalwhich is output as a light detection signal; identification signalreading means for reproducing the identification signal from the lightdetection signal; a first tracking error detection circuit fordetecting, while the optical spot travels on the groove track or theland track, a shift amount of the optical spot with respect to thecenter line and for outputting a first error signal indicating the shiftamount; synchronization signal detection means for detecting from thelight detection signal a point in time at which the beam spot travelsover the synchronization signal section and outputting a referencesignal indicating the point in time; a second tracking error detectioncircuit for detecting, while the optical spot is travelling over theservo control region, a shift amount of the optical spot with respect tothe center line based on the reference signal and the light detectionsignal and for outputting a second error signal indicating the shiftamount; synthesizing means for outputting a tracking signal based on thefirst error signal and the second error signal; and a trackingcontroller for controlling the transportation means to cause the beamspot to travel over the groove track or the land track based on thetracking signal.

In one embodiment of the invention, the synthesizing means outputs asignal obtained by adding the second error signal to the first errorsignal as the third error signal.

In another embodiment of the invention, the synthesizing means includes:identification signal region detection means for detecting whether ornot the beam spot is travelling over the identification signal regionand outputting a region detection signal while the beam spot istravelling over the identification signal region; and error signalretention means for retaining the third error signal while the regiondetection signal is output.

In still another embodiment of the invention, the second tracking errordetection means derives a difference between a d.c. component of thelight detection signal obtained after the lapse of a first tine intervalfrom a point in time at which the reference signal is input and a d.c.component of the light detection signal obtained after the lapse of asecond time interval from the point in time and generates the seconderror signal based on the difference.

In still another embodiment of the invention, the light detection meansincludes two light receiving portions disposed symmetrically withrespect to a direction across the groove track and the land track, eachlight receiving portion converting a received light amount into anelectric signal; the first tracking error detection means includesdifferential operation means for deriving a difference between theelectric signals output from the two light receiving portions; and thesecond tracking error detection means includes addition operation meansfor deriving a sum of the electric signals output from the two lightreceiving portions; and

In still another embodiment of the invention, the optical informationrecording/reproduction device further includes: recording means forrecording an information signal on the groove track or the land track;recording control means for controlling the recording means so as not torecord the information signal in the identification signal region.

Alternatively, the present invention provides an optical informationrecording medium including at least one groove track and at least oneland track allowing information to be recorded on or reproduced from thegroove track and the land track, the groove track and the land trackadjoining each other, wherein the optical information recording mediumfurther includes: a pre-pit array indicating identification informationconcerning the groove track and the land track; and a plurality of pitsdisposed ahead of the pre-pit array along the groove track and the landtrack, the plurality of pits indicating a reproduction synchronizationsignal for reproducing the identification information of the pre-pitarray, the plurality of pits indicating the reproduction synchronizationsignal being positioned so as to shift to opposite sides of a centerline of either the groove track or the land track.

In one embodiment of the invention, the groove track and the land trackare divided into a plurality of sectors, the pre-pit array in theidentification signal region includes an address pit array indicatingaddress information of a corresponding sector.

Alternatively, the present invention provides an optical informationrecording/reproduction device for recording/reproducing information witha light beam on an optical information recording medium including atleast one groove track and at least one land track allowing informationto be recorded on or reproduced from the groove track and the landtrack, the groove track and the land track adjoining each other, and theoptical information recording medium further including: a pre-pit arrayindicating identification information concerning the groove track andthe land track; and a plurality of pits disposed ahead of the pre-pitarray along the groove track and the land track, the plurality of pitsindicating a reproduction synchronization signal for reproducing theidentification information of the pre-pit array, the plurality of pitsindicating the reproduction synchronization signal being positioned soas to shift to opposite sides of a center line of either the groovetrack or the land track, wherein the optical informationrecording/reproduction device includes a circuit for correcting atracking offset based on the plurality of pits indicating thereproduction synchronization signal.

Alternatively, the present invention provides an optical informationrecording medium including information tracks including at least onegroove track and at least one land track formed in a spiral orconcentric shape on a disk substrate, the optical information recordingmedium including at least one zone composed of a plurality ofinformation tracks, wherein the optical information recording mediumfurther includes: a servo control region defined by a meandering portionof the groove track, the meandering portion having at least one meander;an identification signal region including one pre-pit indicating anidentification signal provided for a pair consisting of adjoining onesof the groove track and the land track, the center lines of some or allof the pre-pits being shifted away from the center line of either thegroove track or the land track along a direction across the groove trackand the land track; and an information signal region in which aninformation signal is recorded by irradiation of a light beam, the aninformation signal region being distinct form the identification signalregion.

Alternatively, the present invention provides an optical informationrecording medium including at least one groove track and at least oneland track allowing information to be recorded on or reproduced from thegroove track and the land track, the groove track and the land trackadjoining each other, the optical information recording medium furtherincluding: an identification signal region including a pre-pit arrayindicating identification information concerning the groove track andthe land track; and an information signal region in which an informationsignal is recorded by irradiation of a light beam, wherein the pre-pitarray indicating the identification signal includes: a field numberpre-pit indicating a field number representing the order of informationfields composed of a pair consisting of adjoining ones of the groovetrack and the land track; and a track identification pre-pit fordetecting whether a beam spot created on the optical informationrecording medium by the light beam is currently travelling over thegroove track or the land track, wherein the field number pre-pit isformed substantially on a border line between the groove track and theland track included in each information field, the field number pre-pitbeing provided with a period twice as large as a track pitch along adirection perpendicular to the groove track and the land track, and thetrack identification pre-pit is formed substantially on a border linebetween two adjoining information fields, the track identificationpre-pit being provided with a period four as large as the track pitchalong the direction perpendicular to the groove track and the landtrack.

In one embodiment of the invention, the track identification pre-pitincludes: a first track identifier disposed on the same line as thefield number pre-pit array; a second track identifier disposed ahead ofthe first track identifier along the track direction and located betweenthe first track identifiers adjoining each other along the directionperpendicular to the groove track and the land track.

In another embodiment of the invention, the optical informationrecording medium further includes a rewritable recording layer, whereinthe recording layer is formed of a phase-change type material capable oftaking an amorphous state or a crystal state.

Alternatively, the present invention provides an optical informationrecording/reproduction device for recording/reproducing information witha light beam on an optical information recording medium including atleast one groove track and at least one land track allowing informationto be recorded on or reproduced from the groove track and the landtrack, the groove track and the land track adjoining each other, theoptical information recording medium further including: anidentification signal region including a pre-pit array indicatingidentification information concerning the groove track and the landtrack; and an information signal region in which an information signalis recorded by irradiation of a light beam, wherein the pre-pit arrayindicating the identification signal includes: a field number pre-pitindicating a field number representing the order of information fieldscomposed of a pair consisting of adjoining ones of the groove track andthe land track; and a track identification pre-pit for detecting whethera beam spot created on the optical information recording medium by thelight beam is currently travelling over the groove track or the landtrack, wherein the field number pre-pit is formed substantially on aborder line between the groove track and the land track included in eachinformation field, the field number pre-pit being provided with a periodtwice as large as a track pitch along a direction perpendicular to thegroove track and the land track, and the track identification pre-pit isformed substantially on a border line between two adjoining informationfields, the track identification pre-pit being provided with a periodfour as large as the track pitch along the direction perpendicular tothe groove track and the land track, wherein the optical informationrecording/reproduction device includes: an optical system for allowingthe light beam emitted from a light source to be incident on the opticalinformation recording medium; light detection means for receiving thelight beam reflected from the optical information recording medium andconverting the reflected light into an electric signal which is outputas a light detection signal; identification signal reading means forreproducing the identification signal from the light detection signaland outputting at least the field number; and track identifier detectionmeans for outputting an identifier detection signal in the case where asignal from the track identification pre-pit is detected.

Thus, the invention described herein makes possible the advantages of:(1) providing an optical information recording medium utilizinginformation tracks composed of grooves and lands previously formed onthe optical information recording medium, which does not require anunduly high accuracy of track serve control; and (2) providing anoptical information recording/reproduction device for recording aninformation signal on such an optical information recording medium.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a magnified plan view showing an essential portion of theoptical disk according to an example of the present invention.

FIG. 2 is a view showing the configuration of information tracks of theoptical disk shown in FIG. 1.

FIG. 3 is a diagram describing the sector format of the optical diskshown in FIG. 1.

FIG. 4 is a block diagram showing the configuration of an opticalinformation recording/reproduction device for the optical disk shown inFIG. 1.

FIG. 5 is a block diagram illustrating an essential portion of a devicefor producing the optical disk shown in FIG. 1.

FIG. 6 is a magnified plan view showing an essential portion of theoptical disk according to another example of the present invention.

FIG. 7 is a magnified plan view showing an essential portion of theoptical disk according to still another example of the presentinvention.

FIG. 8 is a magnified plan view showing an essential portion of theoptical disk according to still another example of the presentinvention.

FIG. 9 is a magnified perspective view showing a conventional opticaldisk.

FIG. 10 is a magnified perspective view showing an optical disk in whichinformation is recorded in both lands and grooves.

FIG. 11 is a magnified plan view showing an essential portion of theoptical disk according to Example 5 of the present invention.

FIG. 12 is a view showing the configuration of information tracks of theoptical disk shown in FIG. 11.

FIG. 13 is a diagram describing the sector format of the optical diskshown in FIG. 11.

FIG. 14A is a magnified plan view showing an identification signalsection of the optical disk shown in FIG. 11.

FIG. 14B is a waveform diagram describing a reproduced signal of thereflected light of a beam spot.

FIG. 15 is a block diagram showing the configuration of an opticalinformation recording/reproduction device for the optical disk shown inFIG. 11.

FIG. 16 is a block diagram showing the configuration of anidentification detection circuit according to Example 5.

FIG. 17 is a timing diagram showing various signals in theidentification detection circuit according to Example 5.

FIG. 18 is a flowchart showing an algorithm for determining whether acurrently traced track is a land or a groove according to Example 5.

FIG. 19 is a magnified plan view showing an essential portion of theoptical disk according to Example 6 of the present invention.

FIG. 20 is a magnified plan view showing an essential portion of theoptical disk according to Example 7 of the present invention.

FIG. 21 is a magnified plan view showing an essential portion of theoptical disk according to Example 8 of the present invention.

FIG. 22A is a magnified plan view showing an identification signalsection of the optical disk shown in FIG. 21.

FIG. 22B is a waveform diagram describing a reproduced signal of thereflected light of a beam spot.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the optical information recording medium and the opticalinformation recording/reproduction device of the present invention willbe described by way of examples, with reference to the accompanyingfigures.

In the examples described below, a recordable/reproducible optical diskwill be illustrated which employs a phase-change type recording material(such that recording can be made based on changes in the reflectioncoefficient thereof). The examples will also be directed to a case wherethe angular velocity (CAV) method is employed as a method forcontrolling the rotation of the optical disk.

However, the present invention is applicable to any optical informationrecording medium which at least utilizes lands and grooves. For example,the optical information recording medium does not have to be of areflection type but can also be a transmission type. Moreover, thepresent invention is applicable to recording media on which informationcan be recorded by optical means, e.g., those which are recordable bythe phase-change method, the magnetooptical method, and the organic dyemethod.

EXAMPLE 1

Hereinafter, a first example of the present invention will be describedwith reference to FIG. 1.

FIG. 1 is a magnified plan view showing an essential portion of theoptical disk according to the present example.

In FIG. 1, reference numerals 1, 3, 5, and 7 denote grooves; 2, 4, and 6denote lands; 8 denotes a pre-pit; 9 denotes a beam spot. The lands andthe grooves have substantially the same width.

A region 10 is defined as a synchronization signal section. No groove isformed within the region 10, but pre-pits are formed so as to be onimaginary extensions of the grooves. The pre-pits in the region 10 havea larger width than the other pre-pits in FIG. 1.

The pre-pits are formed to have a depth equal to the difference inheight between the grooves and the lands. The depth of each groove canbe prescribed at any value between about λ/10 and about λ/4 in terms ofoptical length (where λ represents the wavelength of the laser lightused for reading out information on the optical disk). In particular,the groove depth is preferably between about λ/7 and about λ/5 in orderto reduce crosstalk occurring between adjoining tracks, as described inJapanese Laid-Open Patent Publication No. 5-282705.

A region 11 is defined as a wobble pit section. In this region, too, nogroove is formed, but pre-pits are provided so as to wobble to theright/left and the front/back (along the tracing direction by the beamspot 9) with respect to a center line of each information track.

As shown in FIG. 1, the pre-pits form two discrete groups (14 and 15)regarding their positions along the longitudinal direction of theinformation tracks. Hereinafter, the pre-pits 14 which are to be tracedearlier by the beam spot 9 traveling on the tracks in the direction ofan arrow in FIG. 1 will be referred to as the "first wobble pits", andthe pre-pits 15 which are to be traced later by the beam spot 9 than thefirst wobble pits will be referred to as the "second wobble pits".

The first wobble pits and the second wobble pits are shared by adjoininginformation tracks. Therefore, when the beam spot 9 traces a land, thefirst wobble pits 14 are situated on the left of the direction of thetravel of the beam spot 9 (indicated by the arrow in FIG. 1). On theother hand, when the beam spot 9 traces a groove, the first wobble pits14 are situated on the right of the direction of the travel of the beamspot 9.

Similarly, when the beam spot 9 traces a land, the second wobble pits 15are situated on the right of the direction of the travel of the beamspot 9 (indicated by the arrow). On the other hand, when the beam spot 9traces a groove, the second wobble pits 15 are situated on the left ofthe direction of the travel of the beam spot 9. Thus, a tracking erroramount can be detected based on a difference between the amount ofreturned light obtained when the beam spot 9 is on the first wobble pitsand the amount of returned light obtained when the beam spot 9 is on thesecond wobble pits. The principle of the tracking error amount detectionis described in more detail in Japanese Laid-Open Patent Publication No.61-224145, for example.

A region 12 is defined as an identification signal section. No groove isformed in the region 12. If at all, pre-pits representing identificationsignals are formed for every other track so as to be located between thecenter line of a groove and the center line of a land (the presence ofsuch a pre-pit would indicate, for example, logical "1", whereas theabsence of such a pre-pit would indicate, for example, logical "0"). The"identification signals" as used herein refer to various identificationsignals employed for a general optical information recording medium,such as track and/or sector locational information signals (indicatinglocations on the recording medium), sector marks, and referencesynchronization signals.

When a beam spot passes over the identification signal section, aportion of the beam spot travels over the pre-pits for both lands andgrooves. Therefore, the amount of reflected light is modulated by thepre-pit array. Thus, the identification signals can be reproduced forboth lands and grooves.

A region 13 is defined as a main information signal section. As inconventional optical disks, recording pits are formed in the maininformation signal section in accordance with information signals ofvideo, audio or computer data, etc. The dot-dash lines 19 indicate therespective center lines of grooves and lands. Gaps G1 and G2 are formedbefore and after the wobble pit section 11, respectively.

The wobble pit section 11 is located before the identification signalsection 12, rather than immediately before the main information signalsection 13. Thus, the tracking error signal correction (which isperformed by utilizing the wobble pit section 11) is started before thetracking error signal begins to have disturbances due to the pre-pits ofthe identification signal section 12. As a result, the disturbance inthe tracking error signal due to the pre-pits of the identificationsignal section 12 is minimized.

If the wobble pit section 11 is located after the identification signalsection 12, the tracking error signal cannot be sufficiently correctedbecause the tracking error signal correction starts only after thetracking error signal begins to have disturbances due to the pre-pits ofthe identification signal section 12. Moreover, in such cases, the beamspot 9 arrives at the main information signal section 13 beforecompleting the tracking error signal correction, so that there may stillbe a tracking offset left at the beginnings of the main informationsignal section 13.

In the optical disk of the present example, one complete round of atrack is divided into a plurality of sectors. The synchronization signalsection 10, the wobble pit section 11, and the identification signalsection 12 as shown in FIG. 1 are provided at the beginning of eachsector. In the case of a CAV control system, the sectors are disposedradially along the radius direction of the disk. It is also applicableto combine a number of tracks to form one zone, thereby dividing thedisk into a plurality of such zones, and perform a CAV control for eachzone.

Next, the track format of the optical disk of the present example willbe described. FIG. 2 is a view showing the configuration of informationtracks of the optical disk. The optical disk in FIG. 2 includes grooves16 and lands 17. Information track numbers (T, T+1, T+2, T+3, T+4, etc.)are sequentially assigned to the respective rounds of tracks,irrespective of whether they are lands or grooves.

A beam spot travels anticlockwise from the inner periphery to the outerperiphery of the disk.

Each track is divided into a number N of sectors 18, the sectors beingsequentially numbered as 1^(st) to N^(th).

Since the information tracks form a spiral as a whole, the N^(th) sectorin a T^(th) track lies continuously with the 1^(st) sector of a T+2^(th)track in the grooves. Similarly, in the lands, the N^(th) sector in aT+1^(th) track lies continuously with the 1^(st) sector of a T+3^(th)track. These information track numbers and the sector numbers havepreviously been formed in the form of pre-pits as described above.

In the present example, the address data in the "groove" tracks isrecorded in the form of pre-pits. In the case where a "land" track istraced in this configuration, the information of a given location isobtained simply by adding one to the track number of the address dataobtained by reproducing the pre-pits. Since the same sector number isshared by adjoining sectors along the radius direction of the disk,signals obtained by reproducing the pre-pits in the "groove" and "land"information tracks can be equally used as locational information.

FIG. 3 is a diagram describing the format of identification signalscorresponding to one sector. As shown in FIG. 3, one sector consists ofa synchronization signal section, a wobble pit section, anidentification signal section, and a main information signal section.The identification signal section further includes blocks indicating: asector mark, a synchronization pattern, an address mark, a track number,and a sector number, respectively. The functions of the respectiveblocks are as follows:

1) Sector mark: indicates a beginning of a sector

2) Synchronization pattern: generates a block for address datareproduction.

3) Address mark: indicates a beginning of address data.

4) Track number, sector number: indicate address data.

Among the above, the sector mark, the synchronization pattern, and theaddress mark are fixed or identical in all sectors.

Next, an optical information recording/reproducing device capable ofrecording, reproducing or erasing information signals on the opticaldisk according to the present example will be described with referenceto FIG. 4.

An optical disk 21 shown in FIG. 4 has the above-described structure,including "land" and "groove" information tracks 22. Information can berecorded on or reproduced form the optical disk 21 by using the opticalinformation recording/reproducing device in FIG. 4.

First, the structure of an optical head 29 will be described. Theoptical head 29 includes a semiconductor laser element 23, a collimatinglens 24 for collimating laser light emitted from the semiconductor laserelement 23, a half mirror 25, an objective lens 26 for converging thecollimated light led through the half mirror 25 onto an informationsurface of the optical disk 21, an optical detector 27 for receivinglight reflected from the optical disk 21 via the objective lens 26 andthe half mirror 25, and an actuator 28 supporting the objective lens 26.The optical detector 27 includes to light receiving portions 27a and 27bfor generating a tracking error signal, the light receiving portions 27aand 27b defining two integral portions of the optical detector 27divided in parallel to the direction of tracks on the optical disk 21.These elements of the optical head 29 are mounted on a head base (notshown).

The outputs of the optical pickup 29 (i.e., detected signals output fromthe light receiving portions 27a and 27b of the optical detector 27) areinput to a differential amplifier 30 and an addition amplifier 37. Theoutput of the differential amplifier 30 is input to a low-pass filter(LPF) 31. The LPF 31 receives a differential signal from thedifferential amplifier 30, and outputs a signal S1 to a polarityinversion circuit 32. The polarity inversion circuit 32 receives thesignal S1 from the LPF 31 and a control signal L4 from a systemcontroller 56 (described later), and outputs a signal S2 to asynthesizing circuit 33.

On the other hand, the output of the addition amplifier 37 (an additionsignal) is coupled to a high-pass filter (HPF) 38. The HPF 38 outputshigh frequency components of the addition signal to a first waveformshaping circuit 39, a second waveform shaping circuit 42, and asynchronization signal detection circuit 45. The first waveform shapingcircuit 39 receives the high frequency components of the addition signalfrom the HPF 38 and outputs a digital signal to a reproduced signalprocessing circuit 40 (described later). The reproduced signalprocessing circuit 40 outputs a reproduced information signal to anoutput terminal 41. The second waveform shaping circuit 42 receives thehigh frequency components of the addition signal from the HPF 38 andoutputs a digital signal to an address reproduction circuit 43(described later). The address reproduction circuit 43 receives thedigital signal from the second waveform shaping circuit 42, and outputsfirst address data to an address calculation circuit 44 (describedlater). The address calculation circuit 44 receives the first addressdata from the address reproduction circuit 43 and a control signal L1from the system controller 56, and outputs second address data to thesystem controller 56.

The synchronization signal detection circuit 45 receives the highfrequency components of the addition signal from the HPF 38 and outputsa detected synchronization signal to a timing generation circuit 46. Thetiming generation circuit 46 receives the detected synchronizationsignal and outputs a timing pulse to a sample/hold circuit 47. Thesample/hold circuit 47 receives the addition signal from the additionamplifier 37 and the timing pulse from the timing generation circuit 46,and outputs a sampling signal to a correction signal generation circuit48. The correction signal generation circuit 48 receives the samplingsignal from the sample/hold circuit 47, and outputs a correction signalS4 to the correction signal generation circuit 48.

The synthesizing circuit 33 receives the signal S2 from the polarityinversion circuit 32 and the signal S4 from the correction signalgeneration circuit 48, and outputs a signal S3 to a tracking controlcircuit 34.

The tracking control circuit 34 receives the signal S3 from thesynthesizing circuit 33 and the control signal L1 from the systemcontroller 56, and outputs a tracking control signal to one of the twoinput terminals of a first selector 35. The first selector 35 receivesthe tracking control signal from the tracking control circuit 34, adriving pulse from a jump pulse generation circuit 49, and a controlsignal L5 from the system controller 56, so as to output a drivingsignal to a driving circuit 36 and a traverse control circuit 50.

The driving circuit 36 receives the driving signal from the firstselector 35, and outputs a driving current to the actuator 28.

When the main information signal reproduced from recording marks and theidentification signals reproduced from pre-pits have differentreproduction amplitude levels, the first waveform shaping circuit 39 andthe second waveform shaping circuit 42 are adapted to have differentgains.

The jump pulse generation circuit 49 receives a control signal L2 fromthe system controller 56 and outputs a driving pulse to the firstselector 35.

The traverse control circuit 50 receives a control signal L2 from thesystem controller 56 and the tracking control signal from the firstselector 35, and outputs a driving current to a traverse motor 51.

The traverse motor 51 moves the optical head 29 along the radiusdirection of the optical disk 21. A spindle motor 52 rotates the opticaldisk 21.

A recording signal processing circuit 53 receives information signals(e.g., audio/video signals and computer data) via an external inputterminal 54 and a control signal L3 from the system controller 56, andoutputs a recording signal to a laser driving circuit 55 (describedlater). The laser driving circuit 55 receives the control signal L3 fromthe system controller 56 and the recording signal from the recordingsignal processing circuit 53, and outputs a driving current to thesemiconductor laser element 23.

The system controller 56 receives the second address data from theaddress calculation circuit 44. The system controller 56 outputs thecontrol signal L2 to the tracking control circuit 34, the control signalL2 to the traverse control circuit 50, the control signal L3 to therecording signal processing circuit 53 and the laser driving circuit 55,the control signal L4 to the polarity inversion circuit 32 and theaddress calculation circuit 44, the control signal L5 to the firstselector 35, and the control signal L6 to the jump pulse generationcircuit 49.

Next, the operations of the above-described optical informationrecording/reproduction device will be described with reference to FIG.4.

First, the operation of reproducing information signals will bedescribed.

The laser driving circuit 55 is placed in a reproduction mode by thecontrol signal L3 from the system controller 56, and supplies a drivingcurrent to the semiconductor laser 23 so that the semiconductor laser 23is driven to emit light at a predetermined intensity. The traversecontrol circuit 50 outputs a driving current to the traverse motor 51 inaccordance with the control signal L2 from the system controller 56 soas to move the optical head 29 to a target track.

A laser beam emitted from the semiconductor laser 23 is collimated bythe collimating lens 24, led through the beam splitter (half mirror) 25,and converged on the optical disk 21 by the objective lens 26.

A light beam reflected from the optical disk 21, carrying theinformation in the information tracks 22 through diffraction, is ledthrough the objective lens 26 so as to be incident on the opticaldetector 27 due to the beam splitter 25.

The light receiving portions 27a and 27b convert the intensity variationof the incident light beam into electric signals, and outputs theelectric signals to the differential amplifier 30 and the additionamplifier 37. The differential amplifier 30 subjects the input currentsto an I-V (current to voltage) conversion and thereafter takes adifference therebetween, so as to output the difference as adifferential signal.

The LPF 31 extracts the low frequency components of the differentialsignal, and outputs the low frequency components as the signal S1 to thepolarity inversion circuit 32. In accordance with the control signal L4input from the system controller 56, the polarity inversion circuit 32either allows the signal S1 to pass (as the signal S2) or inverts thepolarities (i.e., plus or minus) thereof and outputs the result as thesignal S2 to the synthesizing circuit 53.

For the sake of convenience of description, it is assumed herein thatthe signal S1 is allowed to pass in the case where the target track(i.e., the track carrying information to be recorded or reproduced) is agroove and that the signal S1 is inverted in the case where the targettrack is a land.

The synthesizing circuit 33 adds the signal S4 from the correctionsignal generation circuit 48 to the signal S2 so as to output the resultas the signal S3 to the tracking control circuit 34. Herein, the signalS2 is a so-called "push-pull tracking error signal" which corresponds tothe tracking error amount between the beam spot converged on theinformation surface of the optical disk 21 and the center of the targetinformation track. The signal S4 (which will be described later)corresponds to the offset amount of the push-pull signal. Thesynthesizing circuit 33 cancels the redundant offset components in thesignal S2 by adding the signal S4 thereto.

The tracking control circuit 34 outputs a tracking control signal to thedriving circuit 36 via the first selector 35 in accordance with thelevel of the input signal S3. The driving circuit 36 supplies a drivingcurrent to the actuator 28 in accordance with the tracking controlsignal, whereby the position of the objective lens 26 is controlledalong the direction across the information track 22. As a result, thebeam spot property scans the center of the information track 22.

The traverse control circuit 50 receives the tracking control signal,and drives the traverse motor 51 in accordance with the low frequencycomponents of the tracking control signal so as to gradually move theoptical head 29 along the radius direction of the optical disk 21 as thereproduction operation proceeds.

The first selector 35 connects/disconnects the output of the jump pulsegeneration circuit 49 to/from the input of the driving circuit 36 inaccordance with the control signal L5 from the system controller 56. Thecontrol signal L5 controls the first selector 35 so as to couple theoutput of the jump pulse generation circuit 49 to the input of thedriving circuit 36 only when moving the beam spot between informationtracks, that is, when a "track jump" is made. Otherwise, the firstselector 35 couples the input of the driving circuit 36 to the trackingcontrol circuit 34.

On the other hand, a focus control circuit (not shown) controls theposition of the objective lens 26 along a direction perpendicular to thedisk surface so that the beam spot accurately focuses on the opticaldisk 21.

Once the beam spot is accurately positioned on the information track 22,the addition amplifier 37 subjects the output currents from the lightreceiving portions 27a and 27b to a I-V conversion, and thereafter addsthe converted currents to output the result as an addition signal to theHPF 38.

The HPF 38 cuts off the unnecessary low frequency components of theaddition signal, and allows the reproduced signals (i.e., the maininformation signal and the address signal) as signals having analogwaveforms, which are output to the first waveform shaping circuit 39,the second waveform shaping circuit 42, and the synchronization signaldetection circuit 45.

The second waveform shaping circuit 42 subjects the address signalhaving an analog waveform to a data slice process using a secondthreshold value, thereby converting the address signal into a signalhaving a pulse waveform, which is output to the address reproductioncircuit 43.

The address reproduction circuit 43 demodulates the input digitaladdress signal, and outputs the demodulated digital address signal asthe first address data to the address calculation circuit 44.

The address calculation circuit 44 determines whether the trackcurrently scanned by the beam spot is a land or a groove based on thecontrol signal L4. If the currently scanned track is a land, the addresscalculation circuit 44 adds one to the track number contained in thefirst address data and outputs the result, along with the second number,as the second address data to the system controller 56.

Based on the second address signal, the system controller 56 determineswhether or not the beam spot is on a target address. If the beam spot ison the target address, the control signals L4 and L5 are maintained sothat the beam spot proceeds to trace the main information signalsection. While the beam spot traces the main information signal section,the first waveform shaping circuit 39 subjects the main informationsignal having an analog waveform (which is received via the opticaldetector 27, the addition amplifier 37, and the HPF 38) to a data sliceprocess using a first threshold value, thereby converting the maininformation signal into a digital signal, which is output to thereproduced signal processing circuit 40.

The reproduced signal processing circuit 40 demodulates the inputdigital main information signal, and subjects the demodulated digitalmain information signal to appropriate processes (e.g., errorcorrection) before it is output at the output terminal 41.

When the beam spot travels over the synchronization signal section, thesynchronization signal detection circuit 45 detects a synchronizationsignal from reproduced signals (received via the optical detector 27,the addition amplifier 37, and the HPF 38), and outputs the detectedsynchronization signal to the timing generation circuit 46. Uponreceiving the detected synchronization signal, the timing generationcircuit 46 outputs two timing pulses T1 and T2, at a predetermined timeinterval, to the sample/hold circuit 47.

The timing pulses T1 and T2 are adapted so that the timing pulse T1 isoutput when the beam spot is directly above the first wobble pits 14 andthat the timing pulse T2 is output when the beam spot is directly abovethe second wobble pits 15, in view of the distance between the firstwobble pits 14 and the synchronization signal and the distance betweenthe second wobble pits 15 and the synchronization signal on the disk 21,and the travelling speed of the beam spot.

The gap G1 in FIG. 1 is prescribed to be a distance which is travelledby the beam spot 9 after the beam spot 9 passes over the synchronizationsignal section 10 and before a synchronization signal is detected andtiming pulses are output by the timing generation circuit 46.

When the timing pulse T1 or T2 is input to the sample/hold circuit 47,the same/hold circuit 47 sample and holds the voltage value of theaddition signal input from the addition amplifier 37 at that moment, andcorrespondingly outputs a sampling signal SP1 or SP2 to the correctionsignal generation circuit 48.

The correction signal generation circuit 48 takes a difference betweenthe sampling signals SP1 and SP2, and amplifies or attenuates thedifference by a predetermined gain AG1 so as to output the result to thesynthesizing circuit 33 as the correction signal S4. The synthesizingcircuit 33 cancels the residual offset components in the push-pullsignal S2 input from the polarity inversion circuit 32 by adding thecorrection signal S4 thereto, so as to output the signal S3 to thetracking control circuit 34. The signal S3 is a tracking error signalhaving an improved accuracy as compared to that of the signal S2.

The residual offset components in the push-pull signal S2, which arecancelled in the above operation, typically emerge due to a tilt of theoptical disk 21 along the radius direction, for example. If such anoffset component is present in the DC offset of the signal S2, it isimpossible to completely eliminate the tracking error between the beamspot 9 and the center line of the target information track by trackingcontrol using only the signal S2. According to the present invention,until beam spot 9 has travelled past the identification signal section12, the signal S3 is maintained at the value taken immediately beforethe beam spot 9 started travelling over the identification signalsection 12. As a result, the tracking error signal is prevented fromhaving a large variation at the identification signal section due to anoffset of the beam spot 9 from the pre-pits. Therefore, the beam spot 9stably and accurately traces the center line 19 of the informationtrack. Moreover, the residual offset correction using the correctionsignal S4 is performed before the beam spot 9 arrives at theidentification signal section, so that the identification signals can bestably read out.

The gap G2 in FIG. 1 is prescribed to be equal to a distance which istravelled by the beam spot 9 after the beam spot 9 has gone past thesecond wobble pits 15 and before the synthesizing circuit 33 outputs thecorrection signal S4. Thus, the beam spot 9 does not start tracing theidentification signal section 12 until the residual offset in thetracking control has been removed. As a result, the beginning portion ofthe identification signal section 12 is prevented from being misdetecteddue to an off-tracking.

During recording, the system controller 56 informs the recording signalprocessing circuit 53 and the laser driving circuit 55 with the controlsignal L3 that the operation is in a recording mode.

The recording signal processing circuit 53 adds an error correctioncode, etc., to an audio signal and the like which are input via theexternal input terminal 54, and outputs the signal as an encodedrecording signal to the laser driving circuit 55. Once the laser drivingcircuit 55 is placed in a recording mode by the control signal L3, thelaser driving circuit 55 modulates a driving current applied to thesemiconductor laser 23 in accordance with the recording signal. As aresult, the intensity of the beam spot 9 radiated onto the optical disk21 changes in accordance with the recording signal, whereby recordingpits are formed.

During reproduction, on the other hand, the control signal L3 places thelaser driving circuit 55 in a reproduction mode, and the laser drivingcircuit 55 controls the driving current so that the semiconductor laser23 emits light with a constant intensity which is lower than the lightintensity during the recording mode.

While the above operations are performed, the spindle motor 52 rotatesthe optical disk 21 at a constant angular velocity.

Next, an operation of moving the beam spot 9 to a target address(hereinafter referred to as a "seek operation") will be described inmore detail.

Once an address is designated from which to startrecording/reproduction, the system controller 56 determines whether thesector of the designated address is included in a land track or a groovetrack (by referring to an address map or the like), and outputs thejudgment result as the control signal L4.

Herein, it is assumed that the control signal L4 is at a Lo (Low) levelwhen the sector having the designated address is in a groove, and a Hi(High) level when the sector of the designated address is in a land. Thepolarity inversion circuit 32 inverts the polarities of the input signalif the start address is an address within a land. The polarity inversioncircuit 32 does not invert the polarities of the input signal if thestart address is an address within a groove. The system controller 56supplies the control signal L5 to the first selector 35 so that thetracking control circuit 34 is selected as the input source of thedriving circuit 36. At this time, the tracking control circuit 34 iscontrolled by the control signal L1 not to output a tracking controlsignal.

Next, the control signal L2 is sent to the traverse control circuit 50so as to drive the traverse motor 51 for a "coarse" seek movement. This"coarse" seek movement is made by previously calculating the number oftracks present between the current address (i.e., the address before themovement) and the target address, based on the values of the current andtarget addresses, and comparing the pre-calculated number with thenumber of tracks traversed during the movement (which is derived fromthe tracking error signal).

Then, the control signal L1 causes the tracking control circuit 34 tooutput a tracking control signal to the driving circuit 36 and thetraverse control circuit 50, so that the beam spot 9 roughly traces aland or a groove. Once a tracking lock-in procedure is complete, addressdata from the identification signal section is reproduced. That is, thefirst address data is input to the address calculation circuit 44 viathe optical detector 27, the addition amplifier 37, the HPF 38, thesecond waveform shaping circuit 42, and the address reproduction circuit43.

The address calculation circuit 44 regards the first address data as thecurrent address while the control signal L4 is at the Lo level, andoutputs the first address data as the second address data to the systemcontroller 56. On the other hand, while the control signal L4 is at theHi level, the address calculation circuit 44 adds one to the tracknumber in the address data, and outputs the result as the second addressdata to the system controller 56.

The system controller 56 compares the second address data against thetarget address value. If there is a difference of 1 track or morebetween the track number in the second address data and that of thetarget address value, the system controller 56 causes the first selector35 to couple the output of the jump pulse generation circuit 49 with theinput of the driving circuit 36 based on the control signal L5. Inaddition, the system controller 56 causes the traverse control circuit50 not to output a driving signal to the traverse motor 51 by using thecontrol signal L2. Subsequently, the system controller 56 causes thejump pulse generation circuit 49 to output a driving pulse to drivingcircuit 36 based on the control signal L6, the driving pulsecorresponding to the above-mentioned difference in track numbers.

The driving circuit 36 supplies a driving current corresponding to thedriving pulse to the actuator 28, and causes the beam spot 9 to make a"track jump" by a designated number of tracks. Once the track jump bythe designated number of tracks is complete, then a tracking lock-inprocedure is performed, and after the beam spot 9 has arrived at thetarget sector due to the rotation of the optical disk 21, therecording/reproduction of information signals is started in this sector.

The optical disk 21 according to the present example can be produced byapplying the method described in Japanese Laid-Open Patent PublicationNo. 50-68413, for example. A device for producing the optical disk 21 ofthe present example will now be briefly described with reference to FIG.5. FIG. 5 is a block diagram illustrating the device.

In the device shown in FIG. 5, a radiation beam source 60 (e.g., a laserlight source) emits a radiation beam with sufficient energy. Theradiation beam travels through a light intensity modulator 62, anoptical deflector 63, and a mirror prism 64 so as to be converged onto aminute radiation beam spot by the objective lens 65. A radiation beamsensing layer 67 (e.g., a photoresist layer) is applied on a recordingmedium 66 (e.g., an optical disk substrate).

The light intensity modulator 62 occasionally interrupts the radiationbeam in accordance with identification signals input from anidentification signal generator 68 via an amplifier 69. As a result, theidentification signals output from the identification signal generator68 are converted into radiation beam pulses, which in turn are convertedinto a pit array on the radiation beam sensing layer 67 through reactionto light. The identification signal generator 68 generates anidentification signal when a gate pulse from a gate signal generator 70is input thereto. The light intensity modulator 62 can be composed of,for example, a photoelectric crystal which rotates the deflectiondirection of a radiation beam responsive to a voltage applied theretoand an optical analyzer for converting changes of the direction of thedeflection plane into changes in light intensity.

The optical deflector 63 varies the angle of the radiation beam by avery small angle, only while a gate pulse from the gate signal generator70 is input to the optical deflector 63 via an amplifier 71, so that theminute radiation beam spot is moved on the recording medium 66 by apredetermined width along the radius direction.

The gate signal generator 70 outputs a gate pulse (having a length equalto that of an identification signal section) to the identificationsignal generator 68 and the amplifier 71 at a predetermined period insynchronization with a rotation phase signal output from a motor 72 forrotating the recording medium 66. Thus, a continuous track is written onthe radiation beam sensing layer 67 with no gate pulses being generated.On the other hand, when a gate pulse is generated, an identificationsignal is written in the form of a pit array at a position away from thecontinuous track by a predetermined length along the radius direction.

Thus, a continuous track and a pre-pit array of identification signalscan be written on the radiation beam sensing layer 67 in one sequence ofsteps. In other words, the identification signals are presented in theform of disruptions between continuous tracks. If it is desirable toform a large pre-pit 8 (such as the pre-pits in the synchronizationsignal section 10), the intensity of the radiation beam can be increasedby corresponding amount. After the writing process is complete, stepsincluding etching, transcription, and molding are performed, whereby adisk substrate is accomplished.

EXAMPLE 2

Although the optical disk of Example 1 illustrated in FIG. 1 includesthe gaps G1 and G2 provided before and after the wobble pit section 11,it is also applicable to form, as shown in FIG. 6, a wobble pit section11 adjoining a sector mark block 81 of wide pits, thereby omitting thegap G2.

The sector marks are fixed patterns, and therefore identical regardlessof the track, e.g., between adjoining tracks. Therefore, even if thebeam spot 9 goes off the track center, the beam spot 9 will still bepartially on the adjoining sector mark, thereby reducing the liabilityof misdetecting sector marks. Moreover, the synthesizing circuit 33outputs the signal S3 before the beam spot 9 has travelled past thesecond mark block, so that the residual offset in the tracking controlis eliminated. By adopting wide pits 81 for the sector mark pre-pits asshown in FIG. 6, the detection accuracy of sector marks can be furtherenhanced.

Among the various blocks in the identification signal sectionillustrated in FIG. 3, the synchronization pattern, the address mark,and the sector number are also identical regardless of the track.Therefore, the detector of these pre-pits can also be further enhancedby adopting wide pits for such pre-pits.

EXAMPLE 3

It is also applicable to provide wobble pits immediately after the maininformation signal section consisting of lands and grooves. FIG. 7illustrates an example of such configuration. Reference number 82denotes a wobble pit section including a number of pairs (four pairs inFIG. 7) consisting of first wobble pits and second wobble pits. Thefirst pair serves the function of the synchronization signal section 10in FIG. 1. The first and second wobble pits are both disposed betweenthe center lines of adjoining information tracks so that a half of thebeam spot traces on the wobble pits. Therefore, these wobble pits can bedetected in the same manner as the pre-pits of the identification signalsection 12.

By adopting wobble pits for the synchronization pre-pits, it becomesunnecessary to employ wide pits such as those shown in FIG. 1, therebyfacilitating the production of the disk.

It is also applicable to employ a plurality of wobble pits so as toenable plural times of detection of the residual offset in trackingcontrol. In this case, the accuracy of residual offset detectionimproves so that the beam spot can trace the track center even moreaccurately, thereby improving the tracking control stability and thedetection accuracy of identification signals.

Although the pre-pits of the identification signal section 12 areprovided between the center lines of lands and grooves in the opticaldisk of the present example, the pre-pits of the identification signalsection 12 do not have to be provided exactly in the middle between thecenter lines of lands and grooves, but may be slightly shifted towardthe groove or the land. In such cases, the amplitude of the reproducedwaveforms of the identification signals may vary depending on whetherthey correspond to a land or a groove, but an appropriate waveformshaping can be achieved in either case, by switching between two levelsof threshold values (i.e., one for the lands and the other for thegrooves) in the data slicing performed in the second waveform shapingcircuit.

For example, in the case where the disk substrate has been produced insuch a manner that the pre-pits are shifted toward a land from the exactmiddle between the land and the groove, the amplitudes of the reproducedidentification signals become larger in the lands than in the grooves.Therefore, it is desirable to accordingly increase the threshold valuefor the lands.

Such an optical disk results in a smaller disturbance in the push-pulltracking error signal than in the case where the pre-pits in theidentification signal section 12 are disposed in the exact middlebetween a land and a groove, and therefore contributes to a more stabletracking control.

EXAMPLE 4

Although the detection of the residual offset in tracking control wasbased on the wobble pits provided on the optical disk in Example 3, thesame effect can also be attained by meandering (wobbling) the groovestoward right and left. Specifically, the offset amount between the beamspot and a given information track can be detected by utilizing themodulation component of the returned light due to the meandering of theinformation track as scanned by the beam spot. Hereinafter, theprinciple thereof will be described with reference to FIG. 8.

FIG. 8 is a magnified plan view showing an essential portion of anoptical disk having meandering grooves. In FIG. 8, a region 83 isdefined as a synchronization signal section, and a region 84 is definedas a wobble groove section. The grooves in both regions 83 and 84 aremeandering.

The grooves in the synchronization signal section 83 meander with aperiod corresponding to the pre-pits in the synchronization signalsection 10 shown in FIG. 1. The grooves in the wobble groove section 84meander with a period equal to that period of the wobbling pre-pits inthe wobble pit section 11 shown in FIG. 1.

The amount of reflected light becomes maximum when the center of thebeam spot 9 is at the center of a target groove or land. Therefore, theresidual offset in tracking control can be detected by sampling andcomparing the amount of light reflected from the meandering grooves, asin the case of wobble pits. Moreover, meandering grooves also provide anadvantage in that the grooves are not disrupted during the residualoffset detection, thereby preventing the reflected light amount fromhaving a large variation. As a result, an even more stable trackingcontrol can be attained.

The synchronization signal can be detected by merely monitoring apush-pull signal because the grooves meander in only one direction inthe synchronization section. On the other hand, the grooves in thewobble groove section can have a plurality of meanders. The accuracy ofresidual offset detection can be improved by conducting a plurality ofsamplings.

Wt in FIG. 8 defines a length over which the grooves meander away fromthe track centers. The value of Wt is preferably longer than thediameter of the beam spot and shorter than the minimum length followableby the tracking control for the following reasons: If the length Wt isshorter than the diameter of the beam spot, the reflected light amountis not sufficiently modulated. If the length Wt is longer than theminimum length followable by the tracking control, the beam spot willalso meander along the groove or land so that the reflected light amountis not sufficiently modulated.

In general, the amplitude Wr of the meanders of the grooves shown inFIG. 8 should be 1/4 or less of the groove pitch, and preferably 1/4.

The timing detection for sampling residual offsets can be made bydetecting the meanders of the grooves in the wobble groove section 84and synchronously detecting the output of the addition amplifier 37(FIG. 4), instead of detecting the synchronization signal in thesynchronization signal section 83. Thus, the synchronization signalsection 83 becomes unnecessary so that the area of the main informationsignal section 13 (FIG. 1), and hence the capacity of the optical disk,can be increased.

As for the optical disk substrate, a substrate made of glass,polycarbonate, acryl, or the like can be used. An acryl substrate ispreferably for the following reason: As the present inventors describedin Japanese Laid-Open Patent Publication No. 6-338064, there is a majorproblem of diffusion of heat to adjoining tracks during the recording ofinformation in both lands and grooves of a rewritable recording medium.Such heat diffusion can be minimized by adopting a steep groove edge sothat the recording layer is disrupted or extremely thin at the edgeportion. Such grooves with steep edges are relatively easy to producefrom acryl, due to its good transcribability.

Although the depth of the pre-pits was described to be equal to thedepth of the grooves in Examples 1 to 4, it is also applicable to adopta different depth for the pre-pits. By prescribing the pre-pit depth tobe λ/4, in particular, the beam spot can acquire a large diffractioneffect so that the degree of modulation of identification signals andthe like can be increased.

EXAMPLE 5

FIG. 11 is a magnified plan view showing an essential portion of anoptical information recording medium according to Example 5 of theinvention. As shown in FIG. 11, grooves 101, 103, 105, 107, . . . etc.,and lands 102, 104, 106, 108, . . . etc., are alternately formed in aspiral shape on a disk substrate, thereby constituting informationtracks. Herein, the grooves 101, 103, 105, 107, . . . etc., and thelands 102, 104, 106, 108, . . . etc., are formed so as to havesubstantially the same width. The depth of each groove can be prescribedat any value between about λ/10 and about λ/4 in terms of optical length(where λ represents the wavelength of the laser light used for readingout information on the optical disk). In particular, the groove depth ispreferably between about λ/7 and about λ/5 in order to reduce crosstalkoccurring between adjoining tracks, as described in Japanese Laid-OpenPatent Publication No. 5-282705.

A region 111 is defined as an identification signal section. No grooveis formed in the region 111. If at all, pre-pits 109 representingidentification signals are formed for every other track so as to belocated between the center line 115 of a groove and the center line 115of a land (the presence of such a pre-pit would indicate, for example,logical "1", whereas the absence of such a pre-pit would indicate, forexample, logical "0"). The pre-pits 109 are formed to have a depth equalto the difference in height between the grooves and the lands. Since"tracks" refer to both grooves and lands (i.e., not only grooves), thetrack pitch is half of the groove pitch.

Since the pre-pits 109 indicating identification signals are formed forevery other track so as to be located between the center line 115 of agroove and the center line 115 of a land, when a beam spot 110 passesover the identification signal section 111, a portion of the beam spot110 travels over the pre-pits 109 for both lands and grooves. Therefore,the amount of reflected light is modulated by the pre-pits 109. Thus,the identification signals can be reproduced for both lands and grooves.

A region 112 is defined as a field number section constituting a portionof the identification signal section 111. Herein, a "field" refers to apair consisting of a land and a groove adjoining each other. One fieldreceives one field number the field number sequentially increasing fromthe inner periphery or the outer periphery of the optical disk. In FIG.11, the groove 101 and 102 are combined as a field 116; the groove 103and 104 are combined as a field 117; the groove 105 and 106 are combinedas a field 118; and the groove 107 and 108 are combined as a field 119.Thus, the pre-pits 109 in the field number section 112 are formed on theborder lines between the lands and grooves belonging to the same fields.

A region 113 is defined as a track identification section constituting aportion of the identification signal section 111. In the trackidentification section 113, at least one track identification pre-pit124 is formed for every other field so as to be located between theextensions of the pre-pit arrays in the field number section 112. Inother words, the track identification pre-pits 124 in the trackidentification section 113 are located on border lines between twoadjoining fields. By thus providing the track identification pre-pits124 in the track identification section 113, it becomes possible todetermine whether the beam spot 110 is tracing a land or a groove basedon the reflected light of the beam spot 110 based on the principledescribed in more detail later.

A region 114 is defined as a main information signal section. As inconventional optical disks, recording pits in an amorphous state areformed in the main information signal section 114 in accordance withinformation signals of video, audio or computer data, etc.

Next, the track format of the optical disk of the present example willbe described. FIG. 12 is a view showing the configuration of informationtracks of the optical disk. The optical disk in FIG. 12 includes grooves120 and lands 121 alternately formed in a spiral shape. Field numbers(M-1, M, M+1, M+2, etc.) are sequentially assigned to the respectivefields, the field numbers increasing one by one from the inner peripherytoward the outer periphery.

A beam spot travels anticlockwise from the inner periphery to the outerperiphery of the disk, for example.

Each track is divided into a number N of sectors 122, the sectors beingsequentially numbers as 1^(st) to N^(th).

Since the grooves 120 and the land 121 are formed in a spiral shape, theN^(th) sector in an M^(th) field lies continuously with the 1^(st)sector of an M+1^(th) field.

The above-mentioned field numbers and the sector numbers are formed inthe form of pre-pits 109 and 124 in the identification signal section111 in FIG. 11. In the case of a CAV control system, the sectors aredisposed radially along the radius direction of the disk. It is alsoapplicable to combine a number of tracks to form one zone, therebydividing the disk into a plurality of such zones, and perform a CAVcontrol for each zone.

FIG. 13 is a diagram describing the format of identification signalscorresponding to one sector. As shown in FIG. 13, one sector consists ofan identification signal section and a main information signal section.The identification signal section further includes blocks indicating: asector mark, a synchronization pattern, an address mark, a field number,a sector number, and a track identification section, respectively. Thefunctions of the respective blocks are as follows:

1) Sector mark: indicates a beginning of a sector

2) Synchronization pattern: generates a clock for address datareproduction.

3) Address mark: indicates a beginning of address data.

4) Field number, sector number: indicate address data.

5) Track identification section: distinguish between lands and grooves

Among the above, the sector mark, the synchronization pattern, and theaddress mark are fixed or identical in all sectors. Therefore, even ifthe beam spot 9 goes off the track center in these blocks, the beam spot9 will still be partially on the pre-pits (having the same pattern) inthe adjoining track, thereby reducing the liability of misdetectingthese signals. By adopting wide pits for these pre-pits, the detectionaccuracy of these signals can be further enhanced.

Hereinafter, the principle of determining whether the beam spot 110 istracing a land or a groove at a given moment will be described withrespect to the optical disk according to the present example illustratedin FIG. 11.

FIG. 14A is a magnified view showing the identification signal sectionof the optical disk according to the present example. FIG. 14B is awaveform diagram showing the amount of reflected light when a beam spottraces over the identification signal section. In FIG. 14A, referencenumerals 101, 103, 105, 107, . . . etc., denote grooves, while 102, 104,106, 108, . . . etc., denote lands. Reference numerals 116, 117, 118,119, . . . etc. denote fields. Reference numeral 109 denotes a pre-pitrepresenting field numbers; 110 denotes a beam spot; 112 denotes a fieldnumber section; 113 denotes a track identification section; and 124denotes a track identification pre-pit. These elements are identicalwith those indicated by like numerals in FIG. 11. Lines a and c arecenter lines of the grooves 101 and 103, respectively. Lines b and d arecenter lines of the lands 102 and 104, respectively. In FIG. 14B, Sa,Sb, Sc, and Sd illustrate the waveforms representing the reflected lightamount when the beam spot 110 traces over the center lines a, b, c, andd, respectively, in the direction of the arrow in FIG. 14A.

In the field number section 112, the pre-pits 109 indicating fieldnumbers are formed between the center lines a and b. Therefore, thewaveforms Sa and Sb are identical. On the other hand, in the trackidentification section 113, the track identification pre-pit 124 isformed between the center lines b and c, so that only the waveform Sbhas a peak. In other words, the track identification pre-pit 124 causesa peak only for the land track.

Similarly, in the field number section 112, the pre-pits 109 indicatingfield numbers are formed between the center lines c and d, so that thewaveforms Sc and Sd are identical. However, in the track identificationsection 113, the track identification pre-pit 124 is formed between thecenter lines b and c, so that only the waveform Sc has a peak. In otherwords, the track identification pre-pit 124 causes a peak only for thegroove track. Thus, the reproduction waveforms of the identificationsignal section 111 (FIG. 11) of two information tracks of the same fieldcan be distinguished from each other.

Now, assuming that the field 116 has an odd field number and the field117 has an even field number, it is possible to determine whether acurrently traced track is a land or a groove as follows: Any informationtrack in an odd-numbered field that shows a peak due to the trackidentification pre-pit 124 as the beam spot 110 traces the trackidentification section 113 is a land track, whereas any informationtrack that does not show the above-mentioned peak is a groove track. Inan even-numbered field, on the other hand, any information track thatshows a peak due to the track identification pre-pit 124 as the beamspot 110 traces the track identification section 113 is a groove track,whereas any information track that does not show the above-mentionedpeak is a land track. The track identification pre-pits 124 are providedfor every other field so that the above principle is true of all thefields throughout the optical disk.

Thus, based on the information as to whether a given field number in thefield number section 12 is an even number or an odd number and thepresence/absence of a peak in the reflected light amount due to thetrack identification pre-pit 124, it can be determined whether acurrently traced track is a land or a groove.

Next, an optical information recording/reproducing device capable ofrecording, reproducing or erasing information signals on the opticaldisk according to the present example will be described with referenceto FIG. 15.

FIG. 15 is a block diagram showing an exemplary configuration for theoptical information recording/reproduction device of the presentinvention.

An optical disk 131 shown in FIG. 15 has the above-described structure,including "land" and "groove" information tracks 132. Information can berecorded on or reproduced from the optical disk 131 by using the opticalinformation recording/reproducing device in FIG. 15.

First, the structure of an optical head 139 will be described. Theoptical head 139 includes a semiconductor laser element 133, acollimating lens 134 for collimating laser light emitted from thesemiconductor laser element 133, a half mirror 135, an objective lens136 for converging the collimated light led through the half mirror 135onto an information surface of the optical disk 131, an optical detector137 for receiving light reflected from the optical disk 131 via theobjective lens 136 and the half mirror 135, and an actuator 138supporting the objective lens 136. The optical detector 137 includes twolight receiving portions 137a and 137b for generating a tracking errorsignal, the light receiving portions 137a and 137b defining two integralportions of the optical detector 137 divided in parallel to thedirection of tracks on the optical disk 131. These elements of theoptical head 139 are mounted on a head base (not shown).

The outputs of the optical pickup 139 (i.e., detected signals outputfrom the light receiving portions 137a and 137b of the optical detector137) are input to a differential amplifier 140 and an addition amplifier146. The output of the differential amplifier 140 is input to a low-passfilter (LPF) 141. The LPF 141 receives a differential signal from thedifferential amplifier 140, and outputs a signal S1 to a polarityinversion circuit 142. The polarity inversion circuit 142 receives thesignal S1 from the LPF 141 and a control signal L4 from a systemcontroller 162 (described later), and outputs a signal S2 to a trackingcontrol circuit 143.

On the other hand, the output of the addition amplifier 146 (an additionsignal) is coupled to a high-pass filter (HPF) 147. The HPF 147 outputshigh frequency components of the addition signal to a first waveformshaping circuit 148, a second waveform shaping circuit 151, and aidentifier detection circuit 153. The first waveform shaping circuit 148receives the high frequency components of the addition signal from theHPF 147 and outputs a digital signal to a reproduced signal processingcircuit 149 (described later). The reproduced signal processing circuit149 outputs a reproduced information signal to an output terminal 150.The second waveform shaping circuit 151 receives the high frequencycomponents of the addition signal from the HPF 147 and outputs a digitalsignal to an address reproduction circuit 152 (described later). Theaddress reproduction circuit 152 receives the digital signal from thesecond waveform shaping circuit 151, and outputs first address data toan address calculation circuit 154 (described later).

The identifier detection circuit 153 receives the high frequencycomponents of the addition signal from the HPF 147 and outputs anidentifier detection signal to the address calculation circuit 154.

The address calculation circuit 154 receives the first address data fromthe address reproduction circuit 152 and the identifier detection signalfrom the identifier detection circuit 153, and outputs second addressdata to the system controller 162.

The tracking control circuit 143 receives an output signal from thepolarity inversion circuit 142 and a control signal L1 from the systemcontroller 162, and outputs a tracing control signal to one of the twoinput terminals of a first selector 144. The first selector 144 receivesthe tracking control signal from the tracking control circuit 143, adriving pulse from a jump pulse generation circuit 155, and a controlsignal L5 from the system controller 162, so as to output a drivingsignal to a driving circuit 145 and a traverse control circuit 156.

The driving circuit 145 receives the driving signal from the firstselector 144, and outputs a driving current to the actuator 138.

When the main information signal reproduced from recording marks and theidentification signals reproduced from pre-pits have differentreproduction amplitude levels, the first waveform shaping circuit 148and the second waveform shaping circuit 151 are adapted to havedifferent gains.

The jump pulse generation circuit 155 receives a control signal L6 fromthe system controller 162 and outputs a driving pulse to the firstselector 144.

The traverse control circuit 156 receives a control signal L2 from thesystem controller 162 and the tracking control signal from the firstselector 144, and outputs a driving current to a traverse motor 157.

The traverse motor 157 moves the optical head 139 along the radiusdirection of the optical disk 131. A spindle motor 158 rotates theoptical disk 131.

A recording signal processing circuit 159 receives information signals(e.g., video signals and audio signals) via an external input terminal160 and a control signal L3 from the system controller 162, and outputsa recording signal to a laser driving circuit 161 (described later). Thelaser driving circuit 161 receives the control signal L3 from the systemcontroller 162 and the recording signal from the recording signalprocessing circuit 159, and outputs a driving current to thesemiconductor laser element 133.

The system controller 162 receives the second address data from theaddress calculation circuit 154. The system controller 162 outputs thecontrol signal L1 to the tracking control circuit 143, the controlsignal L2 to the traverse control circuit 156, the control signal L3 tothe recording signal processing circuit 159 and the laser drivingcircuit 161, the control signal L4 to the polarity inversion circuit 142and the address calculation circuit 154, the control signal L5 to thefirst selection 144, and the control signal L6 to the jump pulsegeneration circuit 155.

Next, the operations of the above-described optical informationrecording/reproduction device will be described with reference to FIG.15.

First, the operation of reproducing information signals will bedescribed.

The laser driving circuit 161 is placed in a reproduction mode by thecontrol signal L3 from the system controller 162, and supplies a drivingcurrent to the semiconductor laser 133 so that the semiconductor laser133 is driven to emit light at a predetermined intensity. The traversecontrol circuit 156 outputs a driving current to the traverse motor 157in accordance with the control signal L2 from the system controller 162so as to move the optical head 139 to a target track.

A laser beam emitted from the semiconductor laser 133 is collimated bythe collimating lens 134, led through the beam splitter (half mirror)135, and converged on the optical disk 131 by the objective lens 136.

A light beam reflected from the optical disk 131, carrying theinformation in the information tracks 132 through diffraction (i.e., adistribution of reflected light amount), is led through the objectivelens 136 so as to be incident on the optical detector 137 due to thebeam splitter 135.

The light receiving portions 137a and 137b of the optical detector 137convert the intensity variation of the incident light beam into electricsignals, and outputs the electric signals to the differential amplifier140 and the addition amplifier 146. The differential amplifier 140subjects the input currents to an I-V conversion and thereafter takes adifference therebetween, so as to output the difference as adifferential signal to the LPF 141.

The LPF 141 extracts the low frequency components of the differentialsignal, and outputs the low frequency components as the signal S1 to thepolarity inversion circuit 142. In accordance with the control signal L4input from the system controller 162, the polarity inversion circuit 142either allows the signal S1 to pass (as the signal S2) or inverts thepolarities (i.e., plus or minus) thereof and outputs the result as thesignal S2 to the tracking control circuit 143.

Herein, the signal S2 is a so-called "push-pull tracking error signal"which corresponds to the tracking error amount between the beam spotconverged on the information surface of the optical disk 131 and thecenter of the target information track 132.

For the sake of convenience of description, it is assumed herein thatthe signal S1 is allowed to pass in the case where the target track(i.e., the track carrying information to be recorded or reproduced) is agroove and that the signal S1 is inverted in the case where the targettrack is a land.

The target control circuit 143 outputs a tracking control signal to thedriving circuit 145 via the selector 144 in accordance with the level ofthe input signal S2. The driving circuit 145 supplies a driving currentto the actuator 138 in accordance with the tracking control signal,whereby the position of the objective lens 136 is controlled along thedirection across the information track 132. As a result, the beam spotproperly scans the center of the information track 132.

The traverse control circuit 156 receives the tracking control signal,and drives the traverse motor 157 in accordance with the low frequencycomponents of the tracking control signal so as to gradually move theoptical head 139 along the radius direction of the optical disk 131 asthe reproduction operation proceeds.

The selector 144 connects/disconnects the output of the jump pulsegeneration circuit 155 to/from the input of the driving circuit 145 inaccordance with the control signal L5 from the system controller 162.The control signal L5 controls the selector 144 so as to couple theoutput of the jump pulse generation circuit 155 to the input of thedriving circuit 145 only when moving the beam spot between informationtracks, that is, when a "track jump" is made. Otherwise, the selector144 couples the input of the driving circuit 145 to the tracking controlcircuit 143.

On the other hand, a focus control circuit (not shown) controls theposition of the objective lens 136 along the direction of the opticalaxis so that the beam spot accurately focuses on the optical disk 131.

Once the beam spot is accurately positioned on the information track132, the addition amplifier 146 subjects the output currents from thelight receiving portions 137a and 137b to an I-V conversion, andthereafter adds the converted currents to output the result as anaddition signal to the HPF 147.

The HPF 147 cuts off the unnecessary low frequency components of theaddition signal, and allows the reproduced signals (i.e., the maininformation signal and the address signal) as signals having analogwaveforms, which are output to the first waveform shaping circuit 148,the second waveform shaping circuit 151, and the identifier detectioncircuit 153.

The second waveform shaping circuit 151 subjects the address signalhaving an analog waveform to a data slice process using a secondthreshold value, thereby converting the address signal into a signalhaving a pulse waveform, which is output to the address reproductioncircuit 152.

The address reproduction circuit 152 demodulates the input digitaladdress signal, and outputs a field number and a sector number containedtherein as the first address data to the address calculation circuit154.

The identifier detection circuit 153 detects whether or not thereproduced waveform has a peak due to the track identification pre-pitas the beam spot 110 traces over the track identification section of theoptical disk 131, and outputs the detection result as a digital signalhaving two levels, for example, as an identification detection signal tothe address calculation circuit 154. Herein, it is assumed that theidentification detection signal is at a Hi (High) level when the trackidentification pre-pit is detected, and a Lo (Low) level when no trackidentification pre-pits are detected. The track identification pre-pitcan be detected by using a level comparator, a peak detection circuit,and the like as in the detection of other pre-pits. In the formatstructure shown in FIG. 13, the track identification section is locatedafter the sector number, so that the track identification pre-pit can bedetected by monitoring whether or not the reproduced waveform has a peakdue to the track identification pre-pit after the lapse of apredetermined time from the reading the sector number.

FIG. 16 is a block diagram showing the structure of the identifierdetection circuit. Elements which also appear in FIG. 15 are indicatedby the same reference numerals as used therein. FIG. 17 is a timingchart showing timing pulse signals T1 to T5. As shown in FIG. 16, adetection window generation circuit 170 receives the timing pulse T1from the address reproduction circuit 152, indicating the beginning ofthe reading of the identification signal section. The detection windowgeneration circuit 170 outputs, after a predetermined delay time α, thedetection window signal T2 having a Hi level period of a predetermineddetection window width β to an AND gate 172. The delay time α and thedetection window width β are predetermined so that only the pulse due tothe track identification pre-pit detected by the beam spot 110 fallswithin the Hi level period of the detection window signal T2 in FIG. 17,in view of factors such as the tracking speed of the beam spot 110, andthe rotation variation of the spindle motor 158. On the other hand, athird waveform shaping circuit 171 subjects the reproduced signal fromthe HPF 147 having an analog waveform to a data slicing process using athird threshold value, and thereafter outputs the reproduced signal asthe digital pulse T3 to the AND gate 172. The third threshold value isprescribed to be, for example, about half of the peak voltage so thatthe peak in the signal Sa or Sb due to the pre-pits 124 of the trackidentification section 113, obtained as the beam spot 110 traces overthe track center in FIG. 14, becomes substantially detectable. The ANDgate 172 performs a logical AND operation for the detection windowsignal T2 and the digital pulse T3, and outputs the result as thedigital signal T4 to a latch circuit 173. Once the digital signal T4shifts to the Hi level, the latch circuit 173 retains the Hi level ofthe digital signal T4 and outputs the signal as the identifier detectionsignal T5 to the address calculation circuit 154. The latch circuit 173is reset by means of a timer or the like so that the latch circuit 173does not retain or latch the output signal level any longer after thelapse of an amount of time sufficient for the calculation of the secondaddress data in the address calculation circuit 154.

Although the timing of the generation of the timing pulse T1 wasdescribed to be based on the point of detecting the address mark, thereference point can alternatively be the detection of the sector mark,the field number, or the sector number.

FIG. 18 shows an exemplary algorithm in the address calculation circuit154 for determining whether the currently traced track is a land or agroove. At Step 1, it is determined whether the field number in thefirst address data is an even number or an odd number. If the fieldnumber is an even number, then the control proceeds to Step 2; if thefield number is an odd number, then the control proceeds to Step 4. AtStep 2, it is determined whether the identifier detection signal T5 isat the Hi level or the Lo level. If the identifier detection signal T5is at the Hi level, then the control proceeds to Step 3; if theidentifier detection signal T5 is at the Lo level, then the controlproceeds to Step 5. At Step 4, too, it is determined whether theidentifier detection signal T5 is at the Hi level or the Lo level. Ifthe identifier detection signal T5 is at the Hi level, then the controlproceeds to Step 5; if the identifier detection signal T5 is at the Lolevel, then the control proceeds to Step 3. At Step 3, the currentlytraced track is determined to be a groove. At Step 5, the currentlytraced track is determined to be a land. Thus, the second data isobtained.

Referring back to FIG. 15, the address calculation circuit 154determines whether the track currently scanned by the beam spot is aland or a groove based on the output level of the identifier detectionsignal T5 and on whether the field number of the first address data isodd or even. The address calculation circuit 154 outputs the result,along with the field number and the sector number, as the second addressdata to the system controller 162.

Based on the second address signal, the system controller 162 determineswhether or not the beam spot is on a target address. If the beam spot ison the target address, the control signals L4 and L5 are maintained sothat the beam spot proceeds to trace the main information signalsection. While the beam spot traces the main information signal section,the first waveform shaping circuit 148 subjects the main informationsignal having an analog waveform (which is received via the opticaldetector 137, the addition amplifier 146, and the HPF 147) to a dataslice process using a first threshold value, thereby converting the maininformation signal into a digital signal, which is output to thereproduced signal processing circuit 149.

The reproduced signal processing circuit 149 demodulates the inputdigital main information signal, and subjects the demodulated digitalmain information signal to appropriate processes (e.g., errorcorrection) before it is output at the output terminal 150.

During recording, the system controller 162 informs the recording signalprocessing circuit 159 and the laser driving circuit 161 with thecontrol signal L3 that the operation is in a recording mode.

The recording signal processing circuit 159 adds an error connectioncode, etc., to an audio signal, a video signal, computer data and thelike which are input via the external input terminal 160, and outputsthe signal as an encoded recording signal to the laser driving circuit161. Once the laser driving circuit 161 is placed in a recording mode bythe control signal L3, the laser driving circuit 161 modulates a drivingcurrent applied to the semiconductor laser 133 in accordance with therecording signal. As a result, the intensity of the beam spot 9 radiatedonto the optical disk 131 changes in accordance with the recordingsignal, whereby recording pits are formed.

During reproduction, on the other hand, the control signal L3 places thelaser driving circuit 161 in a reproduction mode, and the laser drivingcircuit 161 controls the driving current so that the semiconductor laser133 emits light with a constant intensity which is lower than the lightintensity during the recording mode.

While the above operations are performed, the spindle motor 158 rotatesthe optical disk 131 at a constant angular velocity.

Next, a seek operation, i.e., an operation of moving the beam spot 9 toa target address, will be described in more detail.

Once an address is designated from which to startrecording/reproduction, the system controller 162 determines whether thesector of the designated address is included in a land track or a groovetrack, and outputs the judgment result as the control signal L4.

Herein, it is assumed that the control signal L4 is at a Lo level whenthe sector having the designated address is in a groove, and a Hi levelwhen the sector of the designated address is in a land. Since thepresent example adopts the push-pull method as the method of trackingerror detection, the polarity of the detected tracking error signalreverses depending on whether the track is a land or a groove.Accordingly, the polarity inversion circuit 142 inverts the polaritiesof the input signal if the start address is an address within a land,and the polarity inversion circuit 142 does not invert the polarities ofthe input signal if the start address is an address within a groove. Thesystem controller 162 supplies the control signal L5 to the selector 144so that the tracking control circuit 143 is selected as the input sourceof the driving circuit 145. At this time, the tracking control circuit143 is controlled by the control signal L1 not to output a trackingcontrol signal.

Next, the control signal L2 is sent to the traverse control circuit 156so as to drive the traverse motor 157 for a "coarse" seek movement. This"coarse" seek movement is made by previously calculating the number oftracks present between the current address (i.e., the address before themovement) and the target address, based on the values of the current andtarget addresses, and comparing the pre-calculated number with thenumber of tracks traversed during the movement (which is derived fromthe tracking error signal).

Then, the control signal L1 causes the tracking control circuit 143 tooutput a tracking control signal to the driving circuit 145 and thetraverse control circuit 156 via the selector 144, so that the beam spot9 roughly traces a lend or a groove. Once a tracking lock-in procedureis complete, address data from the identification signal section isreproduced. That is, the first address data is input to the addresscalculation circuit 154 via the optical detector 137, the additionamplifier 146, the HPF 147, the second waveform shaping circuit 151, andthe address reproduction circuit 152.

The address calculation circuit 154 calculates the second address databased on the input first address data and the identifier detectionsignal from the identifier detection circuit 153, and outputs the secondaddress data to the system controller 162.

The system controller 162 compares the second address data against thetarget address value. If the second address data does not coincide withthe target address value, the system controller 162 causes the selector144 to couple the output of the jump pulse generation circuit 155 withthe input of the driving circuit 145 based on the control signal L5. Inaddition, the system controller 162 causes the traverse control circuit156 not to output a driving signal to the traverse motor 157 by usingthe control signal L2. Subsequently, the system controller 162 causesthe jump pulse generation circuit 155 to output a driving pulse todriving circuit 145 based on the control signal L6, the driving pulsecorresponding to the above-mentioned difference in field numbers.

The driving circuit 145 supplies a driving current corresponding to thedriving pulse to the actuator 138, and causes the beam spot 9 to make a"track jump" by a designated number of tracks. Herein, a "track jump" isdefined as a movement of the beam spot from a groove to a next groove,or from a land to a next land. Once the track jump by the designatednumber of tracks is complete, then a tracking lock-in procedure isperformed, and after the beam spot 9 has arrived at the target sectordue to the rotation of the optical disk 131, the recording/reproductionof information signals is started in this sector.

Although only one track identification pre-pit is provided in theoptical disk of the present example, it is also applicable to provide aplurality of track identification pre-pits, which would reduce theliability of misdetection in track identification, leading to a morereliable detection.

In the case where a plurality of track identification pre-pits areformed, the liability of misdetection in track identification can befurther reduced by ensuring that the track identification pre-pits havea pattern which does not appear in any other signals of theidentification signal section.

EXAMPLE 6

FIG. 19 is a magnified plan view showing an essential portion of anoptical information recording medium according to Example 6 of theinvention. In FIG. 19, reference numerals 101, 103, 105, 107, . . .etc., denote grooves, while 102, 104, 106, 108, . . . etc., denotelands. Reference numeral 109 denotes a pre-pit; 110 denotes a beam spot;111 denotes an identification signal section; 112 denotes a field numbersection; 113 denotes a track identification section; and 114 denotes amain information signal section. These elements are identical with thoseindicated by like numerals in FIG. 11 illustrating Example 5. Referencenumeral 180 denotes a track identification pre-pit. Track identificationpre-pits are arranged in the same manner as the track identificationpre-pits 124 in the track identification section 113 shown in FIG. 11.Reference numeral 181 denotes a groove; 182 denotes a field consistingof the land 102 and the groove 103; 183 denotes a field consisting ofthe land 104 and the groove 105; 184 denotes a field consisting of theland 106 and the groove 107; 185 denotes a field consisting of the land108 and the groove 181. In the present example, the pre-pits 109 in theidentification signal section 111 are all shifted along the radiusdirection of the optical disk by half a groove pitch. Otherwise theoptical disk has the same configuration as that shown in FIG. 11. In thepresent example, as well as Example 5, the lands and the grooves can bedistinguished based on the information as to whether a given fieldnumber is an even number or an odd number and the presence/absence ofthe track identification pre-pit 180.

EXAMPLE 7

FIG. 20 is a magnified plan view showing an essential portion of anoptical information recording medium according to Example 7 of theinvention. In FIG. 20, reference numerals 101, 103, 105, 107, . . .etc., denote grooves, while 102, 104, 106, 108, . . . etc., denotelands. Reference numeral 109 denotes a pre-pit; 110 denotes a beam spot;111 denotes an identification signal section; 112 denotes a field numbersection; 113 denotes a track identification section; and 114 denotes amean information signal section. These elements are identical with thoseindicated by like numerals in FIG. 11 illustrating Example 5. Referencenumeral 190 denotes a track identification pre-pit. Track identificationpre-pits are arranged in the same manner as the track identificationpre-pits 124 in the track identification section 113 shown in FIG. 11.Reference numeral 191 denotes a pre-pit for the generation of timingpulses. The pre-pits 191 are formed on the same line as the pre-pits 109of the field number section 112 with a period equal to the groove pitch.The pre-pits 191 for the generation of timing pulses are located infront of the track identification pre-pits 190 at a distance of γ. Sincethe pre-pits 191 are on the same line as the pre-pits 109 of the fieldnumber section 112, they can be detected regardless of whether the beamspot 110 is tracing on a land or a groove. Therefore, the detectedsignals of the pre-pits 191 can be used as the timing pulse T1 describedin Example 5.

EXAMPLE 8

FIG. 21 is a magnified plan view showing an essential portion of anoptical information recording medium according to Example 8 of theinvention. In FIG. 21, reference numerals 101, 103, 105, 107, . . .etc., denote grooves, while 102, 104, 106, 108, . . . etc., denotelands. Reference numeral 109 denotes a pre-pit; 110 denotes a beam spot;111 denotes an identification signal section; 112 denotes a field numbersection; 113 denotes a track identification section; and 114 denotes amain information signal section. These elements are identical with thoseindicated by like numerals in FIG. 11 illustrating Example 5. Referencenumeral 200 denotes a first track identification pre-pit. One pre-pit200 is formed for every other field so as to be located between theextensions of the pre-pit arrays in the field number section 112.Reference numeral 201 denotes a second track identification pre-pitlocated behind (along the longitudinal direction of the tracks) thefirst identification pre-pits 200. A pair of pre-pits 201 are formed forevery other field so as to be located where the first identificationpre-pits 200 are not located.

FIG. 22A is a magnified view showing the identification number sectionof the optical disk of the present example. FIG. 22B is a waveformdiagram showing the reflected light amount obtained as the beam spot 110traces over the identification signal section. In FIG. 22A, lines a andc are center lines of the grooves 101 and 103, respectively, while linesb and d are center lines of the lands 102 and 104, respectively. In FIG.22B, Sa, Sb, Sc, and Sd illustrate the waveforms representing thereflected light amount when the beam spot 110 traces over the centerlines a, b, c, and d, respectively, in the direction of the arrow inFIG. 22A.

In the field number section 112, the pre-pits 109 indicating fieldnumbers are formed between the center lines a and b. Therefore, thewaveforms Sa and Sb are identical. On the other hand, in the trackidentification section 113, two second track identification pre-pits 201are formed next to the center line a and one first track identificationpre-pit 200 is formed next to the center line b. Therefore, Sa has twopeaks in the track identification section 113, whereas Sb has only onepeek in the track identification section 113.

Similarly, in the track identification section 113, two second trackidentification pre-pits 201 are formed next to the center line d and onefirst track identification pre-pit 200 is formed next to the center linec. Therefore, Sc has one peak in the track identification section 113,whereas Sd has two peaks in the track identification section 113.

Now, assuming that the field 116 has an odd field number and the field117 has an even field number, as in Example 5, it is possible todetermine whether a currently traced track is a land or a groove asfollows: Any information track in an odd-numbered field that shows onepeak in the track identification section 113 is a land track, whereasany information track that shows two peaks in the track identificationsection 113 is a groove track. In an even-numbered field, on the otherhand, any information track in an odd-numbered field that shows one peakin the track identification section 113 is a groove track, whereas anyinformation track that shows two peaks in the track identificationsection 113 is a land track.

Thus, based on the information as to whether a given field number in thefield number section 112 is an even number or an odd number and thenumber of peaks in the reflected light amount in the trackidentification section 113, it can be determined whether a currentlytraced track is a land or a groove.

In the present example, the first and second track identificationpre-pits 200 and 201 cause such peaks regardless of whether the fieldnumber is an even number or an odd number and whether the track is aland or a groove. Therefore, lands and grooves can be accuratelydetermined without misdetection.

Although the pre-pits of the identification signal section 111 areprovided between the center lines of lands and grooves in the opticaldisk of Examples 5 to 8, the pre-pits of the identification signalsection 111 do not have to be provided exactly in the middle between thecenter lines of lands and grooves, but may be slightly shifted towardthe groove or the land. In such cases, the amplitude of the reproducedwaveforms of the identification signals may vary depending on whetherthey correspond to a land or a groove, but an appropriate waveformshaping can be achieved in either case, by switching between two levelsof threshold values (i.e., one for the lands and the other for thegrooves) in the data slicing performed in the second waveform shapingcircuit 151.

For example, in the case where the disk substrate has been produced insuch a manner that the pre-pits are shifted toward a land from the exactmiddle between the land and the groove, the amplitudes of the reproducedidentification signals become larger in the lands than in the grooves.Therefore, it is desirable to accordingly the grooves. Therefore, it isdesirable to accordingly increase the threshold value for the lands.

Such an optical disk results in a smaller disturbance in the push-pullsignal than in the case where the pre-pits in the identification signalsection 111 are disposed in the exact middle between a land and agroove, and therefore contributes to a more stable tracking control.

As for the optical disk substrate, a substrate made of glass,polycarbonate, acryl, or the like can be used. An acryl substrate ispreferable for the following reason: As the present inventors describedin Japanese Laid-Open Patent Publication No. 6-338064, there is a majorproblem of diffusion of heat to adjoining tracks during the recording ofinformation in both lands and grooves of a rewritable recording medium.Such heat diffusion can be minimized by adopting a steep groove edge sothat the recording layer is disrupted or extremely thin at the edgeportion. Such grooves with steep edges are relatively easy to producefrom acryl, due to its good transcribability.

Although the depth of the pre-pits was described to be equal to thedepth of the grooves in Examples 5 to 8, it is also applicable to adopta different depth for the pre-pits. By prescribing the pre-pit depth tobe λ/4, in particular, the beam spot can acquire a large diffractioneffect so that the degree of modulation of identification signals andthe like can be increased.

Although field numbers were assigned to pairs of lands and grooves inthe identification signal section of Examples 5 to 8, it is alsoapplicable to universally number all tracks, without distinguishingbetween lands and grooves. Since the pre-pits in the identificationsignal section correspond to every other track, the track numbers to beformed as the pre-pits in the identification signal section are eitherall numbers or all even numbers. Thus, depending on the determination inthe track identification section as to whether the currently tracedtrack is a land or a groove, the track numbers can be properly known byadding one to the track number obtained from the reproduced pre-pits fora groove, and not adding one to the track number obtained from thereproduced pre-pits for a land.

In the optical disks of Examples 5 to 8, lands and grooves are used asinformation tracks, and each pair consisting of a land and a grooveadjoining each other is defined as one information field. However, anyother configuration can be adopted as long as the track pitch of themain information signal section is half of the track pitch of theidentification signal section (consisting of pre-pits). For example,Examples 5 to 8 are applicable to an magnetooptical disk utilizingmagnetic super-resolution effects.

Thus, according to the present invention, an optical disk with animproved recording density can be provided. For example, it becomespossible to record about the same amount of video information of a laserdisk on a disk of the size of a compact disk (CD), thereby allowing areduction in the size of the optical information recording/reproductiondevice. For example, by employing the above-mentioned opticalinformation recording/reproduction device in place of CD-ROMreproduction devices, which have recently become prevalent in the fieldof personal computers, it becomes possible to record and reproducehigh-quality video data (which requires a large recording capacity) onthe optical disk of any of Examples 1 to 8. Thus, the portability oflarge-capacity information recording media can be improved.

The optical disks used in Examples 1 to 8 typically have the followingdimensions:

groove pitch: 1.48 μm

track pitch: 0.74 μm

groove depth: about 60 to 80 nm

pit depth: about 60 to 80 nm

groove width (land width): 0.6 to 0.7 μm

width of pre-pits in the identification signal section: 0.5 to 0.7 μm

minimum value of length of pre-pits in the identification signalsection: about 0.6 μm

laser light wavelength: 650 nm

numerical aperture (NA) of objective lens: 0.6

It will be appreciated that the present invention is not limited to theabove-mentioned dimensions.

Thus, in accordance with the optical information recording medium andthe optical information recording/reproduction device of the presentinvention, the residual offset in tracking control is cancelled based onwobble pits in a servo region before a beam spot arrives at anidentification signal section consisting of pre-pits disposed off thecenterlines of lands and grooves. Therefore, the beam spot canaccurately trace on the track centers, enabling stable detection ofidentification signals.

Moreover, according to the present invention, it can be determined whichof the two kinds of information tracks the beam spot is currentlytracing on, by detecting the field number and the track identifierformed in the form of pre-pits on a disk substrate. As a result,accurate locational information can be obtained in an opticalinformation recording medium including information tracks with a trackpitch narrower than the minimum track pitch of pre-pits. Thus, anoptical information recording medium with an increased recording densitycan be provided.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. An optical information recording mediumcomprising at least one groove track and at least one land trackallowing information to be recorded on or reproduced from the groovetrack and the land track, the groove track and the land track adjoiningeach other,wherein the optical information recording medium furthercomprises:an identification signal region including a pre-pit array, thepre-pit array indicating identification information concerning thegroove track and the land track, and wherein at least a portion of thepre-pit array in the identification signal region is formed so as to beshifted away from the center line of either the groove track or the landtrack; a servo control region disposed ahead of the identificationsignal region along the groove track and the land track, the servocontrol region including wobble indicia positioned so as to shift toopposite sides of a center line of either the groove track or the landtrack; and a synchronization signal section indicating the beginning ofthe wobble indicia and provided immediately before the wobble indicia.2. An optical information recording medium according to claim 1, whereinthe synchronization signal section includes a pit array positioned onthe center line of either the groove track or the land track.
 3. Anoptical information recording medium according to claim 1, wherein theidentification signal region includes a pit indicating a trackidentification signal.
 4. An optical information recording mediumaccording to claim 3, wherein the pit indicating the trackidentification signal is shifted away from the center line of either thegroove track or the land track.
 5. An optical information recordingmedium according to claim 1, wherein the groove track and the land trackare divided into a plurality of sectors, the pre-pit array in theidentification signal region includes an address pit array indicatingaddress information of a corresponding sector.
 6. An optical informationrecording medium according to claim 1, wherein the groove track and theland track are formed in a spiral or concentric shape on a disksubstrate.
 7. An optical information recording medium according to claim1, wherein the identification information includes a track number.
 8. Anoptical information recording medium according to claim 7, wherein aportion of the pre-pit array indicating the identification signal thatindicates the track number is shifted away from the center line ofeither the groove track or the land track along a direction across thegroove track and the land track.
 9. An optical information recordingmedium according to claim 1, wherein pre-pits in the pre-pit arrayindicating the identification signal which are formed so as to beshifted away from the center line of either the groove track or the landtrack are shifted away from the center line of either the groove trackor the land track by about 1/4 of a groove pitch.
 10. An opticalinformation recording medium according to claim 1, wherein an opticaldepth or height of the pre-pit array indicating the identificationsignal is substantially equal to the depth of the groove track.
 11. Anoptical information recording medium according to claim 1, wherein anoptical depth or height of the pre-pit array indicating theidentification signal is substantially equal to λ/4 (where λ representsthe wavelength of a light beam).
 12. An optical information recordingmedium according to claim 1, wherein the width of the pre-pit arrayindicating the identification signal is substantially equal to the widthof the groove track.
 13. An optical information recording mediumaccording to claim 1, wherein a gap section is provided between theservo control region and the identification signal region.
 14. Anoptical information recording medium according to claim 1 furthercomprising a rewritable recording layer, wherein the recording layer isformed of a phase-change type material capable of taking an amorphousstate or a crystal state.